1
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Kompatscher M, Bartosik K, Erharter K, Plangger R, Juen F, Kreutz C, Micura R, Westhof E, Erlacher M. Contribution of tRNA sequence and modifications to the decoding preferences of E. coli and M. mycoides tRNAGlyUCC for synonymous glycine codons. Nucleic Acids Res 2024; 52:1374-1386. [PMID: 38050960 PMCID: PMC10853795 DOI: 10.1093/nar/gkad1136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Revised: 11/06/2023] [Accepted: 11/10/2023] [Indexed: 12/07/2023] Open
Abstract
tRNA superwobbling, used by certain bacteria and organelles, is an intriguing decoding concept in which a single tRNA isoacceptor is used to decode all synonymous codons of a four-fold degenerate codon box. While Escherichia coli relies on three tRNAGly isoacceptors to decode the four glycine codons (GGN), Mycoplasma mycoides requires only a single tRNAGly. Both organisms express tRNAGly with the anticodon UCC, which are remarkably similar in sequence but different in their decoding ability. By systematically introducing mutations and altering the number and type of tRNA modifications using chemically synthesized tRNAs, we elucidated the contribution of individual nucleotides and chemical groups to decoding by the E. coli and M. mycoides tRNAGly. The tRNA sequence was identified as the key factor for superwobbling, revealing the T-arm sequence as a novel pivotal element. In addition, the presence of tRNA modifications, although not essential for providing superwobbling, was shown to delicately fine-tune and balance the decoding of synonymous codons. This emphasizes that the tRNA sequence and its modifications together form an intricate system of high complexity that is indispensable for accurate and efficient decoding.
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Affiliation(s)
- Maria Kompatscher
- Institute of Genomics and RNomics, Biocenter, Medical University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Karolina Bartosik
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Kevin Erharter
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Raphael Plangger
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Fabian Sebastian Juen
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Christoph Kreutz
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Ronald Micura
- Institute of Organic Chemistry, Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Eric Westhof
- Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire, Architecture et Réactivité de l’ARN, CNRS UPR 9002, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Matthias D Erlacher
- Institute of Genomics and RNomics, Biocenter, Medical University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
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2
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Fages‐Lartaud M, Hundvin K, Hohmann‐Marriott MF. Mechanisms governing codon usage bias and the implications for protein expression in the chloroplast of Chlamydomonas reinhardtii. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2022; 112:919-945. [PMID: 36071273 PMCID: PMC9828097 DOI: 10.1111/tpj.15970] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 08/29/2022] [Accepted: 09/01/2022] [Indexed: 05/30/2023]
Abstract
Chloroplasts possess a considerably reduced genome that is decoded via an almost minimal set of tRNAs. These features make an excellent platform for gaining insights into fundamental mechanisms that govern protein expression. Here, we present a comprehensive and revised perspective of the mechanisms that drive codon selection in the chloroplast of Chlamydomonas reinhardtii and the functional consequences for protein expression. In order to extract this information, we applied several codon usage descriptors to genes with different expression levels. We show that highly expressed genes strongly favor translationally optimal codons, while genes with lower functional importance are rather affected by directional mutational bias. We demonstrate that codon optimality can be deduced from codon-anticodon pairing affinity and, for a small number of amino acids (leucine, arginine, serine, and isoleucine), tRNA concentrations. Finally, we review, analyze, and expand on the impact of codon usage on protein yield, secondary structures of mRNA, translation initiation and termination, and amino acid composition of proteins, as well as cotranslational protein folding. The comprehensive analysis of codon choice provides crucial insights into heterologous gene expression in the chloroplast of C. reinhardtii, which may also be applicable to other chloroplast-containing organisms and bacteria.
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Affiliation(s)
- Maxime Fages‐Lartaud
- Department of BiotechnologyNorwegian University of Science and TechnologyTrondheimN‐7491Norway
| | - Kristoffer Hundvin
- Department of BiotechnologyNorwegian University of Science and TechnologyTrondheimN‐7491Norway
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3
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Ye S, Lehmann J. Genetic code degeneracy is established by the decoding center of the ribosome. Nucleic Acids Res 2022; 50:4113-4126. [PMID: 35325219 PMCID: PMC9023292 DOI: 10.1093/nar/gkac171] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2021] [Revised: 02/10/2022] [Accepted: 03/23/2022] [Indexed: 11/21/2022] Open
Abstract
The degeneracy of the genetic code confers a wide array of properties to coding sequences. Yet, its origin is still unclear. A structural analysis has shown that the stability of the Watson–Crick base pair at the second position of the anticodon–codon interaction is a critical parameter controlling the extent of non-specific pairings accepted at the third position by the ribosome, a flexibility at the root of degeneracy. Based on recent cryo-EM analyses, the present work shows that residue A1493 of the decoding center provides a significant contribution to the stability of this base pair, revealing that the ribosome is directly involved in the establishment of degeneracy. Building on existing evolutionary models, we show the evidence that the early appearance of A1493 and A1492 established the basis of degeneracy when an elementary kinetic scheme of translation was prevailing. Logical considerations on the expansion of this kinetic scheme indicate that the acquisition of the peptidyl transferase center was the next major evolutionary step, while the induced-fit mechanism, that enables a sharp selection of the tRNAs, necessarily arose later when G530 was acquired by the decoding center.
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Affiliation(s)
- Shixin Ye
- INSERM U1195 unit, University of Paris-Saclay, 94276 Le Kremlin Bicêtre, France
| | - Jean Lehmann
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, University of Paris-Saclay, 91198 Gif-sur-Yvette, France
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4
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Fages-Lartaud M, Hohmann-Marriott MF. Overview of tRNA Modifications in Chloroplasts. Microorganisms 2022; 10:226. [PMID: 35208681 PMCID: PMC8877259 DOI: 10.3390/microorganisms10020226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Revised: 01/16/2022] [Accepted: 01/18/2022] [Indexed: 11/29/2022] Open
Abstract
The chloroplast is a promising platform for biotechnological innovation due to its compact translation machinery. Nucleotide modifications within a minimal set of tRNAs modulate codon-anticodon interactions that are crucial for translation efficiency. However, a comprehensive assessment of these modifications does not presently exist in chloroplasts. Here, we synthesize all available information concerning tRNA modifications in the chloroplast and assign translation efficiency for each modified anticodon-codon pair. In addition, we perform a bioinformatics analysis that links enzymes to tRNA modifications and aminoacylation in the chloroplast of Chlamydomonas reinhardtii. This work provides the first comprehensive analysis of codon and anticodon interactions of chloroplasts and its implication for translation efficiency.
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Affiliation(s)
- Maxime Fages-Lartaud
- Department of Biotechnology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway;
| | - Martin Frank Hohmann-Marriott
- Department of Biotechnology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway;
- United Scientists CORE (Limited), Dunedin 9016, Aotearoa, New Zealand
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5
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Cui J, Liu Q, Sendinc E, Shi Y, Gregory RI. Nucleotide resolution profiling of m3C RNA modification by HAC-seq. Nucleic Acids Res 2021; 49:e27. [PMID: 33313824 PMCID: PMC7969016 DOI: 10.1093/nar/gkaa1186] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 11/18/2020] [Accepted: 11/20/2020] [Indexed: 01/27/2023] Open
Abstract
Cellular RNAs are subject to a myriad of different chemical modifications that play important roles in controlling RNA expression and function. Dysregulation of certain RNA modifications, the so-called 'epitranscriptome', contributes to human disease. One limitation in studying the functional, physiological, and pathological roles of the epitranscriptome is the availability of methods for the precise mapping of individual RNA modifications throughout the transcriptome. 3-Methylcytidine (m3C) modification of certain tRNAs is well established and was also recently detected in mRNA. However, methods for the specific mapping of m3C throughout the transcriptome are lacking. Here, we developed a m3C-specific technique, Hydrazine-Aniline Cleavage sequencing (HAC-seq), to profile the m3C methylome at single-nucleotide resolution. We applied HAC-seq to analyze ribosomal RNA (rRNA)-depleted total RNAs in human cells. We found that tRNAs are the predominant m3C-modified RNA species, with 17 m3C modification sites on 11 cytoplasmic and 2 mitochondrial tRNA isoacceptors in MCF7 cells. We found no evidence for m3C-modification of mRNA or other non-coding RNAs at comparable levels to tRNAs in these cells. HAC-seq provides a novel method for the unbiased, transcriptome-wide identification of m3C RNA modification at single-nucleotide resolution, and could be widely applied to reveal the m3C methylome in different cells and tissues.
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Affiliation(s)
- Jia Cui
- Stem Cell Program, Division of Hematology/Oncology, Boston Children's Hospital, Boston, MA 02115, USA.,Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Qi Liu
- Stem Cell Program, Division of Hematology/Oncology, Boston Children's Hospital, Boston, MA 02115, USA.,Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Erdem Sendinc
- Division of Newborn Medicine and Epigenetics Program, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA
| | - Yang Shi
- Division of Newborn Medicine and Epigenetics Program, Department of Medicine, Boston Children's Hospital, Boston, MA 02115, USA.,Ludwig Institute for Cancer Research, Oxford Branch, Oxford University, Oxford OX3 7DQ, UK
| | - Richard I Gregory
- Stem Cell Program, Division of Hematology/Oncology, Boston Children's Hospital, Boston, MA 02115, USA.,Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.,Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA.,Harvard Initiative for RNA Medicine, Boston, MA 02115, USA.,Harvard Stem Cell Institute, Cambridge, MA 02138, USA
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6
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Pernod K, Schaeffer L, Chicher J, Hok E, Rick C, Geslain R, Eriani G, Westhof E, Ryckelynck M, Martin F. The nature of the purine at position 34 in tRNAs of 4-codon boxes is correlated with nucleotides at positions 32 and 38 to maintain decoding fidelity. Nucleic Acids Res 2020; 48:6170-6183. [PMID: 32266934 PMCID: PMC7293025 DOI: 10.1093/nar/gkaa221] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 03/19/2020] [Accepted: 03/25/2020] [Indexed: 12/29/2022] Open
Abstract
Translation fidelity relies essentially on the ability of ribosomes to accurately recognize triplet interactions between codons on mRNAs and anticodons of tRNAs. To determine the codon-anticodon pairs that are efficiently accepted by the eukaryotic ribosome, we took advantage of the IRES from the intergenic region (IGR) of the Cricket Paralysis Virus. It contains an essential pseudoknot PKI that structurally and functionally mimics a codon-anticodon helix. We screened the entire set of 4096 possible combinations using ultrahigh-throughput screenings combining coupled transcription/translation and droplet-based microfluidics. Only 97 combinations are efficiently accepted and accommodated for translocation and further elongation: 38 combinations involve cognate recognition with Watson-Crick pairs and 59 involve near-cognate recognition pairs with at least one mismatch. More than half of the near-cognate combinations (36/59) contain a G at the first position of the anticodon (numbered 34 of tRNA). G34-containing tRNAs decoding 4-codon boxes are almost absent from eukaryotic genomes in contrast to bacterial genomes. We reconstructed these missing tRNAs and could demonstrate that these tRNAs are toxic to cells due to their miscoding capacity in eukaryotic translation systems. We also show that the nature of the purine at position 34 is correlated with the nucleotides present at 32 and 38.
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Affiliation(s)
- Ketty Pernod
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Laure Schaeffer
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Johana Chicher
- Institut de Biologie Moléculaire et Cellulaire, Plateforme Protéomique Strasbourg - Esplanade, CNRS FRC1589, Université de Strasbourg, 2, allée Konrad Roentgen Descartes, F-67084 Strasbourg, France
| | - Eveline Hok
- Laboratory of tRNA Biology, Department of Biology, Rita Liddy Hollings Science Center, 58 Coming Street, Charleston, SC, USA
| | - Christian Rick
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Renaud Geslain
- Laboratory of tRNA Biology, Department of Biology, Rita Liddy Hollings Science Center, 58 Coming Street, Charleston, SC, USA
| | - Gilbert Eriani
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Eric Westhof
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Michael Ryckelynck
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
| | - Franck Martin
- Institut de Biologie Moléculaire et Cellulaire, 'Architecture et Réactivité de l'ARN' CNRS UPR9002, Université de Strasbourg, 2, allée Konrad Roentgen, F-67084 Strasbourg, France
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7
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Rebelo-Guiomar P, Powell CA, Van Haute L, Minczuk M. The mammalian mitochondrial epitranscriptome. BIOCHIMICA ET BIOPHYSICA ACTA. GENE REGULATORY MECHANISMS 2019; 1862:429-446. [PMID: 30529456 PMCID: PMC6414753 DOI: 10.1016/j.bbagrm.2018.11.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 11/16/2018] [Accepted: 11/23/2018] [Indexed: 01/08/2023]
Abstract
Correct expression of the mitochondrially-encoded genes is critical for the production of the components of the oxidative phosphorylation machinery. Post-transcriptional modifications of mitochondrial transcripts have been emerging as an important regulatory feature of mitochondrial gene expression. Here we review the current knowledge on how the mammalian mitochondrial epitranscriptome participates in regulating mitochondrial homeostasis. In particular, we focus on the latest breakthroughs made towards understanding the roles of the modified nucleotides in mitochondrially-encoded ribosomal and transfer RNAs, the enzymes responsible for introducing these modifications and on recent transcriptome-wide studies reporting modifications to mitochondrial messenger RNAs. This article is part of a Special Issue entitled: mRNA modifications in gene expression control edited by Dr. Matthias Soller and Dr. Rupert Fray.
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Affiliation(s)
- Pedro Rebelo-Guiomar
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK; Graduate Program in Areas of Basic and Applied Biology (GABBA), University of Porto, Porto, Portugal
| | | | - Lindsey Van Haute
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK
| | - Michal Minczuk
- MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, UK.
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8
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Agris PF, Eruysal ER, Narendran A, Väre VYP, Vangaveti S, Ranganathan SV. Celebrating wobble decoding: Half a century and still much is new. RNA Biol 2017; 15:537-553. [PMID: 28812932 PMCID: PMC6103715 DOI: 10.1080/15476286.2017.1356562] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 07/04/2017] [Accepted: 07/06/2017] [Indexed: 10/25/2022] Open
Abstract
A simple post-transcriptional modification of tRNA, deamination of adenosine to inosine at the first, or wobble, position of the anticodon, inspired Francis Crick's Wobble Hypothesis 50 years ago. Many more naturally-occurring modifications have been elucidated and continue to be discovered. The post-transcriptional modifications of tRNA's anticodon domain are the most diverse and chemically complex of any RNA modifications. Their contribution with regards to chemistry, structure and dynamics reveal individual and combined effects on tRNA function in recognition of cognate and wobble codons. As forecast by the Modified Wobble Hypothesis 25 years ago, some individual modifications at tRNA's wobble position have evolved to restrict codon recognition whereas others expand the tRNA's ability to read as many as four synonymous codons. Here, we review tRNA wobble codon recognition using specific examples of simple and complex modification chemistries that alter tRNA function. Understanding natural modifications has inspired evolutionary insights and possible innovation in protein synthesis.
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Affiliation(s)
- Paul F. Agris
- The RNA Institute, State University of New York, Albany, NY, USA
- Department of Biology, State University of New York, Albany, NY, USA
- Department of Chemistry, State University of New York, Albany, NY, USA
| | - Emily R. Eruysal
- Department of Biology, State University of New York, Albany, NY, USA
| | - Amithi Narendran
- Department of Biology, State University of New York, Albany, NY, USA
| | - Ville Y. P. Väre
- Department of Biology, State University of New York, Albany, NY, USA
| | - Sweta Vangaveti
- The RNA Institute, State University of New York, Albany, NY, USA
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9
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Fang X, Michnicka M, Zhang Y, Wang YX, Nikonowicz EP. Capture and Release of tRNA by the T-Loop Receptor in the Function of the T-Box Riboswitch. Biochemistry 2017; 56:3549-3558. [PMID: 28621923 PMCID: PMC5813812 DOI: 10.1021/acs.biochem.7b00284] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In Gram-positive bacteria, the tRNA-dependent T-box riboswitch system regulates expression of amino acid biosynthetic and aminoacyl-tRNA synthetase genes through a transcription attenuation mechanism. Binding of uncharged tRNA "closes" the switch, allowing transcription read-through. Structural studies of the 100-nucleotide stem I domain reveal tRNA utilizes base pairing and stacking interactions to bind the stem, but little is known structurally about the 180-nucleotide riboswitch core (stem I, stem III, and antiterminator stem) in complex with tRNA or the mechanism of coupling of the intermolecular binding domains crucial to T-box function. Here we utilize solution structural and biophysical methods to characterize the interplay of the different riboswitch-tRNA contact points using Bacillus subtilis and Oceanobacillus iheyensis glycyl T-box and T-box:tRNA constructs. The data reveal that tRNA:riboswitch core binding at equilibrium involves only Specifier-anticodon and antiterminator-acceptor stem pairing. The elbow:platform stacking interaction observed in studies of the T-box stem I domain is released after pairing between the acceptor stem and the bulge in the antiterminator helix. The results are consistent with the model of T-box riboswitch:tRNA function in which tRNA is captured by stem I of the nascent mRNA followed by stabilization of the antiterminator helix and the paused transcription complex.
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Affiliation(s)
- Xianyang Fang
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China, 100084
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD 21702
| | | | - Yikan Zhang
- Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China, 100084
| | - Yun-Xing Wang
- Structural Biophysics Laboratory, National Cancer Institute, Frederick, MD 21702
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10
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Han L, Marcus E, D'Silva S, Phizicky EM. S. cerevisiae Trm140 has two recognition modes for 3-methylcytidine modification of the anticodon loop of tRNA substrates. RNA (NEW YORK, N.Y.) 2017; 23:406-419. [PMID: 28003514 PMCID: PMC5311504 DOI: 10.1261/rna.059667.116] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 12/12/2016] [Indexed: 05/25/2023]
Abstract
The 3-methylcytidine (m3C) modification is ubiquitous in eukaryotic tRNA, widely found at C32 in the anticodon loop of tRNAThr, tRNASer, and some tRNAArg species, as well as in the variable loop (V-loop) of certain tRNASer species. In the yeast Saccharomyces cerevisiae, formation of m3C32 requires Trm140 for six tRNA substrates, including three tRNAThr species and three tRNASer species, whereas in Schizosaccharomyces pombe, two Trm140 homologs are used, one for tRNAThr and one for tRNASer The occurrence of a single Trm140 homolog is conserved broadly among Ascomycota, whereas multiple Trm140-related homologs are found in metazoans and other fungi. We investigate here how S. cerevisiae Trm140 protein recognizes its six tRNA substrates. We show that Trm140 has two modes of tRNA substrate recognition. Trm140 recognizes G35-U36-t6A37 of the anticodon loop of tRNAThr substrates, and this sequence is an identity element because it can be used to direct m3C modification of tRNAPhe However, Trm140 recognition of tRNASer substrates is different, since their anticodons do not share G35-U36 and do not have any nucleotides in common. Rather, specificity of Trm140 for tRNASer is achieved by seryl-tRNA synthetase and the distinctive tRNASer V-loop, as well as by t6A37 and i6A37 We provide evidence that all of these components are important in vivo and that seryl-tRNA synthetase greatly stimulates m3C modification of tRNASer(CGA) and tRNASer(UGA) in vitro. In addition, our results show that Trm140 binding is a significant driving force for tRNA modification and suggest separate contributions from each recognition element for the modification.
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MESH Headings
- Anticodon/chemistry
- Anticodon/metabolism
- Base Sequence
- Binding Sites
- Cloning, Molecular
- Cytidine/analogs & derivatives
- Cytidine/genetics
- Cytidine/metabolism
- Escherichia coli/genetics
- Escherichia coli/metabolism
- Gene Expression
- Microfilament Proteins/genetics
- Microfilament Proteins/metabolism
- Nucleic Acid Conformation
- Protein Binding
- Protein Biosynthesis
- Protein Domains
- RNA, Transfer, Phe/chemistry
- RNA, Transfer, Phe/genetics
- RNA, Transfer, Phe/metabolism
- RNA, Transfer, Ser/chemistry
- RNA, Transfer, Ser/genetics
- RNA, Transfer, Ser/metabolism
- RNA, Transfer, Thr/chemistry
- RNA, Transfer, Thr/genetics
- RNA, Transfer, Thr/metabolism
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/metabolism
- Saccharomyces cerevisiae Proteins/genetics
- Saccharomyces cerevisiae Proteins/metabolism
- Substrate Specificity
- tRNA Methyltransferases/genetics
- tRNA Methyltransferases/metabolism
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Affiliation(s)
- Lu Han
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester School of Medicine, Rochester, New York 14642, USA
| | - Erin Marcus
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester School of Medicine, Rochester, New York 14642, USA
| | - Sonia D'Silva
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester School of Medicine, Rochester, New York 14642, USA
| | - Eric M Phizicky
- Department of Biochemistry and Biophysics, Center for RNA Biology, University of Rochester School of Medicine, Rochester, New York 14642, USA
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11
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Saint-Léger A, Bello C, Dans PD, Torres AG, Novoa EM, Camacho N, Orozco M, Kondrashov FA, Ribas de Pouplana L. Saturation of recognition elements blocks evolution of new tRNA identities. SCIENCE ADVANCES 2016; 2:e1501860. [PMID: 27386510 PMCID: PMC4928997 DOI: 10.1126/sciadv.1501860] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 03/31/2016] [Indexed: 06/01/2023]
Abstract
Understanding the principles that led to the current complexity of the genetic code is a central question in evolution. Expansion of the genetic code required the selection of new transfer RNAs (tRNAs) with specific recognition signals that allowed them to be matured, modified, aminoacylated, and processed by the ribosome without compromising the fidelity or efficiency of protein synthesis. We show that saturation of recognition signals blocks the emergence of new tRNA identities and that the rate of nucleotide substitutions in tRNAs is higher in species with fewer tRNA genes. We propose that the growth of the genetic code stalled because a limit was reached in the number of identity elements that can be effectively used in the tRNA structure.
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Affiliation(s)
- Adélaïde Saint-Léger
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
| | - Carla Bello
- Bioinformatics and Genomics Programme, Centre for Genomic Regulation, Barcelona Institute of Science and Technology, 88 Dr. Aiguader, 08003 Barcelona, Catalonia, Spain
- Universitat Pompeu Fabra, 08003 Barcelona, Catalonia, Spain
| | - Pablo D. Dans
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
- Joint BSC-IRB Research Program in Computational Biology, Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
| | - Adrian Gabriel Torres
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
| | - Eva Maria Novoa
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
- Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, 32 Vassar Street, Cambridge, MA 02139, USA
- Broad Institute of MIT and Harvard, 415 Main Street, Cambridge, MA 02139, USA
| | - Noelia Camacho
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
| | - Modesto Orozco
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
- Joint BSC-IRB Research Program in Computational Biology, Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
- Departament de Bioquimica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avgda Diagonal 647, 08028 Barcelona, Catalonia, Spain
| | - Fyodor A. Kondrashov
- Bioinformatics and Genomics Programme, Centre for Genomic Regulation, Barcelona Institute of Science and Technology, 88 Dr. Aiguader, 08003 Barcelona, Catalonia, Spain
- Universitat Pompeu Fabra, 08003 Barcelona, Catalonia, Spain
- Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluis Companys 23, 08010 Barcelona, Catalonia, Spain
| | - Lluís Ribas de Pouplana
- Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac 10, 08028 Barcelona, Catalonia, Spain
- Catalan Institution for Research and Advanced Studies (ICREA), Passeig Lluis Companys 23, 08010 Barcelona, Catalonia, Spain
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12
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Köhrer C, Mandal D, Gaston KW, Grosjean H, Limbach PA, Rajbhandary UL. Life without tRNAIle-lysidine synthetase: translation of the isoleucine codon AUA in Bacillus subtilis lacking the canonical tRNA2Ile. Nucleic Acids Res 2013; 42:1904-15. [PMID: 24194599 PMCID: PMC3919564 DOI: 10.1093/nar/gkt1009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Translation of the isoleucine codon AUA in most prokaryotes requires a modified C (lysidine or agmatidine) at the wobble position of tRNA2Ile to base pair specifically with the A of the AUA codon but not with the G of AUG. Recently, a Bacillus subtilis strain was isolated in which the essential gene encoding tRNAIle-lysidine synthetase was deleted for the first time. In such a strain, C34 at the wobble position of tRNA2Ile is expected to remain unmodified and cells depend on a mutant suppressor tRNA derived from tRNA1Ile, in which G34 has been changed to U34. An important question, therefore, is how U34 base pairs with A without also base pairing with G. Here, we show (i) that unlike U34 at the wobble position of all B. subtilis tRNAs of known sequence, U34 in the mutant tRNA is not modified, and (ii) that the mutant tRNA binds strongly to the AUA codon on B. subtilis ribosomes but only weakly to AUG. These in vitro data explain why the suppressor strain displays only a low level of misreading AUG codons in vivo and, as shown here, grows at a rate comparable to that of the wild-type strain.
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Affiliation(s)
- Caroline Köhrer
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA, Department of Chemistry, Rieveschl Laboratories for Mass Spectrometry, University of Cincinnati, Cincinnati, OH 45221, USA and Centre de Génétique Moléculaire, CNRS, Gif-sur-Yvette, F-91198, France
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13
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Chang AT, Nikonowicz EP. Solution nuclear magnetic resonance analyses of the anticodon arms of proteinogenic and nonproteinogenic tRNA(Gly). Biochemistry 2012; 51:3662-74. [PMID: 22468768 DOI: 10.1021/bi201900j] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Although the fate of most tRNA molecules in the cell is aminoacylation and delivery to the ribosome, some tRNAs are destined to fulfill other functional roles. In addition to their central role in translation, tRNA molecules participate in processes such as regulation of gene expression, bacterial cell wall biosynthesis, viral replication, antibiotic biosynthesis, and suppression of alternative splicing. In bacteria, glycyl-tRNA molecules with anticodon sequences GCC and UCC exhibit multiple extratranslational functions, including transcriptional regulation and cell wall biosynthesis. We have determined the high-resolution structures of three glycyl-tRNA anticodon arms with anticodon sequences GCC and UCC. Two of the tRNA molecules are proteinogenic (tRNA(Gly,GCC) and tRNA(Gly,UCC)), and the third is nonproteinogenic (np-tRNA(Gly,UCC)) and participates in cell wall biosynthesis. The UV-monitored thermal melting curves show that the anticodon arm of tRNA(Gly,UCC) with a loop-closing C-A(+) base pair melts at a temperature 10 °C lower than those of tRNA(Gly,GCC) and np-tRNA(Gly,UCC). U-A and C-G pairs close the loops of the latter two molecules and enhance stem stability. Mg(2+) stabilizes the tRNA(Gly,UCC) anticodon arm and reduces the T(m) differential. The structures of the three tRNA(Gly) anticodon arms exhibit small differences among one another, but none of them form the classical U-turn motif. The anticodon loop of tRNA(Gly,GCC) becomes more dynamic and disordered in the presence of multivalent cations, whereas metal ion coordination in the anticodon loops of tRNA(Gly,UCC) and np-tRNA(Gly,UCC) establishes conformational homogeneity. The conformational similarity of the molecules is greater than their functional differences might suggest. Because aminoacylation of full-length tRNA molecules is accomplished by one tRNA synthetase, the similar structural context of the loop may facilitate efficient recognition of each of the anticodon sequences.
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Affiliation(s)
- Andrew T Chang
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77251-1892, United States
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14
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Noma A, Yi S, Katoh T, Takai Y, Suzuki T, Suzuki T. Actin-binding protein ABP140 is a methyltransferase for 3-methylcytidine at position 32 of tRNAs in Saccharomyces cerevisiae. RNA (NEW YORK, N.Y.) 2011; 17:1111-9. [PMID: 21518805 PMCID: PMC3096043 DOI: 10.1261/rna.2653411] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Accepted: 03/09/2011] [Indexed: 05/25/2023]
Abstract
Transfer RNAs contain various modified nucleotides that are introduced enzymatically at the post-transcriptional level. In Saccharomyces cerevisiae, 3-methylcytidine (m³C) is found at position 32 of the tRNAs for Thr and Ser. We used a systematic reverse genetic approach combined with mass spectrometry (ribonucleome analysis), and identified the actin-binding protein ABP140 as the protein responsible for m³C formation in both tRNA(Thr1) and tRNA(Ser1). ABP140 consists of an N-terminal actin-binding sequence and a C-terminal S-adenosylmethionine (Ado-Met) binding motif. Deletion of the actin-binding sequence in ABP140 did not affect m³C formation, indicating that subcellular localization of ABP140 to actin filaments is not involved in tRNA modification. m³C formation in tRNA(Thr1) could be reconstituted using recombinant Abp140p in the presence of Ado-Met, whereas m³C did not form in tRNA(Ser1) in vitro, indicating the absence of a factor(s) required for tRNA(Ser1) m³C formation. Thus, ABP140 has been designated TRM140 according to the preferred nomenclature. In addition, we observed a specific reduction of m³C formation in HeLa cells by siRNA-mediated knock down of the human ortholog of TRM140.
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Affiliation(s)
- Akiko Noma
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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15
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Suzuki T, Nagao A, Suzuki T. Human mitochondrial diseases caused by lack of taurine modification in mitochondrial tRNAs. WILEY INTERDISCIPLINARY REVIEWS-RNA 2011; 2:376-86. [PMID: 21957023 DOI: 10.1002/wrna.65] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mitochondrial DNA mutations that cause mitochondrial dysfunction are responsible for a wide spectrum of human diseases, referred to as mitochondrial diseases. Pathogenic point mutations are found frequently in genes encoding mitochondrial (mt) tRNAs, indicating that impaired functioning of mutant mt tRNAs is the primary cause of mitochondrial dysfunction. Our previous studies revealed the absence of posttranscriptional taurine modification at the anticodon wobble uridine in mutant mt tRNAs isolated from cells derived from patients with two major classes of mitochondrial diseases, MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes) and MERRF (myoclonus epilepsy associated with ragged red fibers). Defective taurine modification of the mutant mt tRNAs results in a deficiency in protein synthesis as the cognate codons of the mutant mt tRNA cannot be decoded. These findings represent the first evidence of a molecular pathogenesis caused by an RNA modification disorder.
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Affiliation(s)
- Tsutomu Suzuki
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Tokyo, Japan.
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16
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Ran W, Higgs PG. The influence of anticodon-codon interactions and modified bases on codon usage bias in bacteria. Mol Biol Evol 2010; 27:2129-40. [PMID: 20403966 DOI: 10.1093/molbev/msq102] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Most transfer RNAs (tRNAs) can translate more than one synonymous codon, and most codons can be translated by more than one isoacceptor tRNA. The rates of translation of synonymous codons are dependent on the concentrations of the tRNAs and on the rates of pairing of each anticodon-codon combination. Translational selection causes a significant bias in codon frequencies in highly expressed genes in most bacteria. By comparing codon frequencies in high and low-expression genes, we determine which codons are preferred for each amino acid in a large sample of bacterial genomes. We relate this to the number of copies of each tRNA gene in each genome. In two-codon families, preferred codons have Watson-Crick pairs (GC and AU) between the third codon base and the wobble base of the anticodon rather than GU pairs. This suggests that these combinations are more rapidly recognized by the ribosome. In contrast, in four-codon families, preferred codons do not correspond to Watson-Crick rules. In some cases, a wobble-U tRNA can pair with all four codons. In these cases, A and U codons are preferred over G and C. This indicates that the nonstandard UU combination appears to be translated surprisingly well. Differences in modified bases at the wobble position of the anticodon appear to be responsible for the differences in behavior of tRNAs in two- and four-codon families. We discuss the way changes in the bases in the anticodon influence both the speed and the accuracy of translation. The number of tRNA gene copies and the strength of translational selection correlate with the growth rate of the organism, as we would expect if the primary cause of translational selection in bacteria is the requirement to optimize the speed of protein production.
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Affiliation(s)
- Wenqi Ran
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada
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17
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Murakami H, Ohta A, Suga H. Bases in the anticodon loop of tRNA(Ala)(GGC) prevent misreading. Nat Struct Mol Biol 2009; 16:353-8. [PMID: 19305404 DOI: 10.1038/nsmb.1580] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2008] [Accepted: 02/13/2009] [Indexed: 11/09/2022]
Abstract
The bases at positions 32 and 38 in the tRNA anticodon loop are known to have a specific conservation depending upon the anticodon triplets. Here we report that evolutionarily conserved pairs of bases at positions 32 and 38 in tRNA(Ala)(GGC) prevent misreading of a near-cognate valine codon, GUC. The tRNA(Ala)(GGC) molecules with the conserved A32-U38 and C32-G38 pairs do not read GUC, whereas those with three representative nonconserved pairs, U32-U38, U32-A38 and C32-A38, direct the misincorporation of alanine at this valine codon into the peptide chain. Overexpression of the nonconserved tRNA(Ala)(GGC) in Escherichia coli is toxic and prevents cell growth. These results suggested that the bases at positions 32 and 38 in tRNA(Ala)(GGC) evolved to preserve the fidelity of the cognate codon reading.
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Affiliation(s)
- Hiroshi Murakami
- Research Center for Advanced Science and Technology, University of Tokyo, Meguro-ku, Tokyo, Japan.
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18
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Atkins JF, Björk GR. A gripping tale of ribosomal frameshifting: extragenic suppressors of frameshift mutations spotlight P-site realignment. Microbiol Mol Biol Rev 2009; 73:178-210. [PMID: 19258537 PMCID: PMC2650885 DOI: 10.1128/mmbr.00010-08] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mutants of translation components which compensate for both -1 and +1 frameshift mutations showed the first evidence for framing malleability. Those compensatory mutants isolated in bacteria and yeast with altered tRNA or protein factors are reviewed here and are considered to primarily cause altered P-site realignment and not altered translocation. Though the first sequenced tRNA mutant which suppressed a +1 frameshift mutation had an extra base in its anticodon loop and led to a textbook "yardstick" model in which the number of anticodon bases determines codon size, this model has long been discounted, although not by all. Accordingly, the reviewed data suggest that reading frame maintenance and translocation are two distinct features of the ribosome. None of the -1 tRNA suppressors have anticodon loops with fewer than the standard seven nucleotides. Many of the tRNA mutants potentially affect tRNA bending and/or stability and can be used for functional assays, and one has the conserved C74 of the 3' CCA substituted. The effect of tRNA modification deficiencies on framing has been particularly informative. The properties of some mutants suggest the use of alternative tRNA anticodon loop stack conformations by individual tRNAs in one translation cycle. The mutant proteins range from defective release factors with delayed decoding of A-site stop codons facilitating P-site frameshifting to altered EF-Tu/EF1alpha to mutant ribosomal large- and small-subunit proteins L9 and S9. Their study is revealing how mRNA slippage is restrained except where it is programmed to occur and be utilized.
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Affiliation(s)
- John F Atkins
- BioSciences Institute, University College, Cork, Ireland.
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19
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Näsvall SJ, Nilsson K, Björk GR. The ribosomal grip of the peptidyl-tRNA is critical for reading frame maintenance. J Mol Biol 2008; 385:350-67. [PMID: 19013179 DOI: 10.1016/j.jmb.2008.10.069] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 10/21/2008] [Accepted: 10/22/2008] [Indexed: 11/15/2022]
Abstract
If a ribosome shifts to an alternative reading frame during translation, the information in the message is usually lost. We have selected mutants of Salmonella typhimurium with alterations in tRNA(cmo5UGG)(Pro) that cause increased frameshifting when present in the ribosomal P-site. In 108 such mutants, two parts of the tRNA molecule are altered: the anticodon stem and the D-arm, including its tertiary interactions with the variable arm. Some of these alterations in tRNA(cmo5UGG)(Pro) are in close proximity to ribosomal components in the P-site. The crystal structure of the 30S subunit suggests that the C-terminal end of ribosomal protein S9 contacts nucleotides 32-34 of peptidyl-tRNA. We have isolated mutants with defects in the C-terminus of S9 that induce +1 frameshifting. Combinations of changes in tRNA(cmo5UGG)(Pro) and S9 suggest that an interaction occurs between position 32 of the peptidyl-tRNA and the C-terminal end of S9. Together, our results suggest that the cause of frameshifting is an aberrant interaction between the peptidyl-tRNA and the P-site environment. We suggest that the "ribosomal grip" of the peptidyl-tRNA is pivotal for maintaining the reading frame.
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MESH Headings
- Frameshifting, Ribosomal
- Models, Molecular
- Mutation, Missense
- Nucleic Acid Conformation
- Point Mutation
- Protein Biosynthesis
- RNA, Messenger/metabolism
- RNA, Transfer, Amino Acyl/genetics
- RNA, Transfer, Amino Acyl/metabolism
- RNA, Transfer, Pro/genetics
- RNA, Transfer, Pro/metabolism
- Reading Frames
- Ribosomal Protein S9
- Ribosomal Proteins/genetics
- Ribosomes/metabolism
- Salmonella typhimurium/physiology
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Affiliation(s)
- S Joakim Näsvall
- Department of Molecular Biology, Umeå University, S-901 87 Umeå, Sweden
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20
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Lehmann J, Libchaber A. Degeneracy of the genetic code and stability of the base pair at the second position of the anticodon. RNA (NEW YORK, N.Y.) 2008; 14:1264-9. [PMID: 18495942 PMCID: PMC2441979 DOI: 10.1261/rna.1029808] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
With an analysis of the structural constraints of the anticodon-codon interaction within the decoding center of the ribosome, we show that the extent of degeneracy at the third position of the anticodon is determined by the level of stability of the base pair at the second position.
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21
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Saks ME, Conery JS. Anticodon-dependent conservation of bacterial tRNA gene sequences. RNA (NEW YORK, N.Y.) 2007; 13:651-60. [PMID: 17379816 PMCID: PMC1852809 DOI: 10.1261/rna.345907] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The residues in tRNA that account for its tertiary fold and for its specific aminoacylation are well understood. In contrast, relatively little is known about the residues in tRNA that dictate its ability to transit the different sites of the ribosome. Yet protein synthesis cannot occur unless tRNA properly engages with the ribosome. This study analyzes tRNA gene sequences from 145 fully sequenced bacterial genomes. Grouping the sequences according to the anticodon triplet reveals that many residues in tRNA, including some that are distal to the anticodon loop, are conserved in an anticodon-dependent manner. These residues evade detection when tRNA genes are grouped according to amino acid family. The conserved residues include those at positions 32, 38, and 37 of the anticodon loop, which are already known to influence tRNA translational performance. Therefore, it seems likely that the newly detected anticodon-associated residues also influence tRNA performance on the ribosome. Remarkably, tRNA genes that belong to the same amino acid family and therefore share identical residues at the second and third anticodon positions have diverged, during bacterial evolution, into highly conserved groups that are defined by the residue at the first (wobble) anticodon position. Current ideas about the properties of tRNA and the translation mechanism do not fully account for this phenomenon. The results of the present study provide a foundation for studying the adaptation of individual tRNAs to the translation machinery and for future studies of the translation mechanism.
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Affiliation(s)
- Margaret E Saks
- Department of Biochemistry, Molecular Biology, and Cell Biology, Northwestern University, Evanston, Illinois 60208, USA.
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22
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Takai K. Classification of the possible pairs between the first anticodon and the third codon positions based on a simple model assuming two geometries with which the pairing effectively potentiates the decoding complex. J Theor Biol 2006; 242:564-80. [PMID: 16764891 DOI: 10.1016/j.jtbi.2006.04.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2005] [Revised: 02/11/2006] [Accepted: 04/11/2006] [Indexed: 11/24/2022]
Abstract
Crick's wobble theory states that some specific pairs between the bases at the first position of the anticodon (position 34) and the third position of the codon (position III) are allowed and the others are disallowed during the correct codon recognition. However, later researches have shown that the pairing rule, or the wobble rule, is different from the supposed one. Despite the continuing efforts including computer-aided model building studies and analyses of three-dimensional structures in the crystals of the ribosomes, the structural backgrounds of the wobble rule are still unclear. Here, I classify the possible pairs into 6 classes according to the increases accompanying the formation of the pairs in the potential productivity of the decoding complex on the basis of a simple model that was originally proposed previously and is refined here. In the model, the conformation with the base at position 34 displaced toward the minor groove side from the position for the Watson-Crick pairs is supposed to be equivalent to the conformation with the Watson-Crick pairs. It is also reasoned and supposed that some weak pairs may sometimes be allowed depending on the structural context. It is demonstrated that most of the experimental results reported so far are consistent with the model. I discuss on which experimental facts can be reasoned with the model and which need further explanations. I expect that the model will be a good basis for further understanding of the wobble rule and its structural backgrounds.
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Affiliation(s)
- Kazuyuki Takai
- Cell-free Science and Technology Research Center, Ehime University, 3, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
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23
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Konevega AL, Soboleva NG, Makhno VI, Peshekhonov AV, Katunin VI. Effect of modification of tRNA nucleotide 37 on the tRNA interaction with the A and P sites of the Escherichia coli 70S ribosome. Mol Biol 2006. [DOI: 10.1134/s0026893306040121] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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24
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Cabello-Villegas J, Nikonowicz EP. Solution structure of psi32-modified anticodon stem-loop of Escherichia coli tRNAPhe. Nucleic Acids Res 2005; 33:6961-71. [PMID: 16377777 PMCID: PMC1322268 DOI: 10.1093/nar/gki1004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Nucleoside base modifications can alter the structures and dynamics of RNA molecules and are important in tRNAs for maintaining translational fidelity and efficiency. The unmodified anticodon stem–loop from Escherichia coli tRNAPhe forms a trinucleotide loop in solution, but Mg2+ and dimethylallyl modification of A37 N6 destabilize the loop-proximal base pairs and increase the mobility of the loop nucleotides. The anticodon arm has three additional modifications, ψ32, ψ39, and A37 C2-thiomethyl. We have used NMR spectroscopy to investigate the structural and dynamical effects of ψ32 on the anticodon stem-loop from E.coli tRNAPhe. The ψ32 modification does not significantly alter the structure of the anticodon stem–loop relative to the unmodified parent molecule. The stem of the RNA molecule includes base pairs ψ32-A38 and U33–A37 and the base of ψ32 stacks between U33 and A31. The glycosidic bond of ψ32 is in the anti configuration and is paired with A38 in a Watson–Crick geometry, unlike residue 32 in most crystal structures of tRNA. The ψ32 modification increases the melting temperature of the stem by ∼3.5°C, although the ψ32 and U33 imino resonances are exchange broadened. The results suggest that ψ32 functions to preserve the stem integrity in the presence of additional loop modifications or after reorganization of the loop into a translationally functional conformation.
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Affiliation(s)
| | - Edward P. Nikonowicz
- To whom correspondence should be addressed. Tel: +1 713 348 4912; Fax +1 713 348 5154;
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25
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Olejniczak M, Dale T, Fahlman RP, Uhlenbeck OC. Idiosyncratic tuning of tRNAs to achieve uniform ribosome binding. Nat Struct Mol Biol 2005; 12:788-93. [PMID: 16116437 DOI: 10.1038/nsmb978] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Accepted: 07/22/2005] [Indexed: 11/09/2022]
Abstract
The binding of seven tRNA anticodons to their complementary codons on Escherichia coli ribosomes was substantially impaired, as compared with the binding of their natural tRNAs, when they were transplanted into tRNA(2)(Ala). An analysis of chimeras composed of tRNA(2)(Ala) and various amounts of either tRNA(3)(Gly) or tRNA(2)(Arg) indicates that the presence of the parental 32-38 nucleotide pair is sufficient to restore ribosome binding of the transplanted anticodons. Furthermore, mutagenesis of tRNA(2)(Ala) showed that its highly conserved A32-U38 pair serves to weaken ribosome affinity. We propose that this negative binding determinant is used to offset the very tight codon-anticodon interaction of tRNA(2)(Ala). This suggests that each tRNA sequence has coevolved with its anticodon to tune ribosome affinity to a value that is the same for all tRNAs.
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Affiliation(s)
- Mikołaj Olejniczak
- Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
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26
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Leipuviene R, Björk GR. A reduced level of charged tRNAArgmnm5UCU triggers the wild-type peptidyl-tRNA to frameshift. RNA (NEW YORK, N.Y.) 2005; 11:796-807. [PMID: 15840821 PMCID: PMC1370764 DOI: 10.1261/rna.7256705] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2004] [Accepted: 01/25/2005] [Indexed: 05/24/2023]
Abstract
Frameshift mutations can be suppressed by a variety of differently acting external suppressors. The +1 frameshift mutation hisC3072, which has an extra G in a run of Gs, is corrected by the external suppressor mutation sufF44. We have shown that sufF44 and five additional allelic suppressor mutations are located in the gene argU coding for the minor tRNAArgmnm5UCU and alter the secondary and/or tertiary structure of this tRNA. The C61U, G53A, and C32U mutations influence the stability, whereas the C56U, C61U, G53A, and G39A mutations decrease the arginylation of tRNAArgmnm5UCU. The T-10C mutant has a base substitution in the -10 consensus sequence of the argU promoter that reduces threefold the synthesis of tRNAArgmnm5UCU . The lower amount of tRNAArgmnm5UCU or impaired arginylation, either independently or in conjunction, results in inefficient reading of the cognate AGA codon that, in turn, induces frameshifts. According to the sequence of the peptide produced from the suppressed -GGG-GAA-AGA- frameshift site, the frameshifting tRNA in the argU mutants is tRNAGlumnm5s2UUC, which decodes the GAA codon located upstream of the AGA arginine codon, and not the mutated tRNAArgmnm5UCU. We propose that an inefficient decoding of the AGA codon by a defective tRNAArgmnm5UCU stalls the ribosome at the A-site codon allowing the wild-type form of peptidyl-tRNAGlumnm5s2UUC to slip forward 1 nucleotide and thereby re-establish the ribosome in the 0-frame. Similar frame-shifting events could be the main cause of various phenotypes associated with environmental or genetically induced changes in the levels of aminoacylated tRNA.
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MESH Headings
- Alleles
- Amino Acid Sequence
- Base Sequence
- Codon/genetics
- Frameshift Mutation/genetics
- Frameshifting, Ribosomal/genetics
- Genes, Bacterial/genetics
- Models, Genetic
- Molecular Sequence Data
- RNA, Transfer, Arg/genetics
- RNA, Transfer, Arg/metabolism
- RNA, Transfer, Glu/genetics
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/genetics
- Salmonella enterica/genetics
- Suppression, Genetic/genetics
- Transfer RNA Aminoacylation
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Affiliation(s)
- Ramune Leipuviene
- Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden
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27
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Yamada Y, Matsugi J, Ishikura H, Murao K. Bacillus subtilis tRNA(Pro) with the anticodon mo5UGG can recognize the codon CCC. ACTA ACUST UNITED AC 2005; 1728:143-9. [PMID: 15833716 DOI: 10.1016/j.bbaexp.2005.02.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2004] [Revised: 02/22/2005] [Accepted: 02/23/2005] [Indexed: 11/17/2022]
Abstract
In Bacillus subtilis, four codons, CCU, CCC, CCA, and CCG, are used for proline. There exists, however, only one proline-specific tRNA having the anticodon mo(5)UGG. Here, we found that this tRNA(Pro)(mo(5)UGG) can read not only the codons CCA, CCG and CCU but also CCC, using an in vitro assay system. This means that the first nucleoside of its anticodon, 5-methoxyuridine (mo(5)U), recognizes A, G, U and C. On the other hand, it was reported that mo(5)U at the first position of the anticodon of tRNA(Val)(mo(5)UAC) can recognize A, G, and U but not C. A comparison of the structure of the anticodon stem and loop of tRNA(Pro)(mo(5)UGG) with those of other tRNAs containing mo(5)U at the first positions of the anticodons suggests that a modification of nucleoside 32 to pseudouridine (Psi) enables tRNA(Pro)(mo(5)UGG) to read the CCC codon.
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Affiliation(s)
- Yuko Yamada
- Department of Biochemistry, Jichi Medical School, 3311-1 Yakushiji, Minamikawachi-machi, Tochigi-ken, 329-0498, Japan.
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28
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Biosynthesis and function of tRNA wobble modifications. FINE-TUNING OF RNA FUNCTIONS BY MODIFICATION AND EDITING 2005. [DOI: 10.1007/b106361] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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29
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Umeda N, Suzuki T, Yukawa M, Ohya Y, Shindo H, Watanabe K, Suzuki T. Mitochondria-specific RNA-modifying Enzymes Responsible for the Biosynthesis of the Wobble Base in Mitochondrial tRNAs. J Biol Chem 2005; 280:1613-24. [PMID: 15509579 DOI: 10.1074/jbc.m409306200] [Citation(s) in RCA: 169] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human mitochondrial (mt) tRNA(Lys) has a taurine-containing modified uridine, 5-taurinomethyl-2-thiouridine (taum5s2U), at its anticodon wobble position. We previously found that the mt tRNA(Lys), carrying the A8344G mutation from cells of patients with myoclonus epilepsy associated with ragged-red fibers (MERRF), lacks the taum5s2U modification. Here we describe the identification and characterization of a tRNA-modifying enzyme MTU1 (mitochondrial tRNA-specific 2-thiouridylase 1) that is responsible for the 2-thiolation of the wobble position in human and yeast mt tRNAs. Disruption of the yeast MTU1 gene eliminated the 2-thio modification of mt tRNAs and impaired mitochondrial protein synthesis, which led to reduced respiratory activity. Furthermore, when MTO1 or MSS1, which are responsible for the C5 substituent of the modified uridine, was disrupted along with MTU1, a much more severe reduction in mitochondrial activity was observed. Thus, the C5 and 2-thio modifications act synergistically in promoting efficient cognate codon decoding. Partial inactivation of MTU1 in HeLa cells by small interference RNA also reduced their oxygen consumption and resulted in mitochondria with defective membrane potentials, which are similar phenotypic features observed in MERRF.
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Affiliation(s)
- Noriko Umeda
- Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Japan
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30
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Duan J, Antezana MA. Mammalian mutation pressure, synonymous codon choice, and mRNA degradation. J Mol Evol 2004; 57:694-701. [PMID: 14745538 DOI: 10.1007/s00239-003-2519-1] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2003] [Accepted: 06/30/2003] [Indexed: 11/29/2022]
Abstract
The usage of synonymous codons (SCs) in mammalian genes is highly correlated with local base composition and is therefore thought to be determined by mutation pressure. The usage is nonetheless structured. For instance, mammals share with Saccharomyces and Drosophila most preferences for the C-ending over the G-ending codon (or vice versa) within each fourfold-degenerate SC family and the fact that their SCs are placed along coding regions in ways that minimize the number of T|A and C|G dinucleotides ("|" being the codon boundary). TA and CG underrepresentations are observed everywhere in the mammalian genome affecting the SC usage, the amino acid composition of proteins, and the primary structure of introns and noncoding DNA. While the rarity of CG is ascribed to the high mutability of this dinucleotide, the rarity of TA in coding regions is considered adaptive because UA dinucleotides are cleaved by endoribonucleases. Here we present in vivo experimental evidence indicating that the number of T|A and/or C|G dinucleotides of a human gene can affect strongly the expression level and degradation of its mRNA. Our results are consistent with indirect evidence produced by other workers and with the detailed work that has been devoted to characterize UA cleavage in vitro and in vivo. We conclude that SC choice can influence strongly mRNA function and gene expression through effects not directly related to the codon-anticodon interaction. These effects should constrain heavily the nucleotide motif composition of the most abundant mRNAs in the transcriptome, in particular, their SC usage, a usage that must be reflected by cellular tRNA concentrations and thus defines for all other genes which SCs are translated fastest and most accurately. Furthermore, the need to avoid such effects genome-wide appears serious enough to have favored the evolution of biases in context-dependent mutation that reduce the occurrence of intrinsically unfavorable motifs, and/or, when possible, to have induced the molecular machinery mediating such effects to rely opportunistically on already existing motif rarities and abundances. This may explain why nucleotide motif preferences are very similar in transcribed and nontranscribed mammalian DNA even though the preferences appear to be adaptive only in transcribed DNA.
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Affiliation(s)
- Jubao Duan
- Department of Psychiatry, The University of Chicago, 924 East 57th Street, R-004, Chicago, IL 60637, USA
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31
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32
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Santos MAS, Moura G, Massey SE, Tuite MF. Driving change: the evolution of alternative genetic codes. Trends Genet 2004; 20:95-102. [PMID: 14746991 DOI: 10.1016/j.tig.2003.12.009] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Pioneering studies in the 1960s that elucidated the genetic code suggested that all extant forms of life use the same genetic code. This early presumption has subsequently been challenged by the discovery of deviations of the universal genetic code in prokaryotes, eukaryotic nuclear genomes and mitochondrial genomes. These studies have revealed that the genetic code is still evolving despite strong negative forces working against the fixation of mutations that result in codon reassignment. Recent data from in vitro, in vivo and in silico comparative genomics studies are revealing significant, previously overlooked links between modified nucleosides in tRNAs, genetic code ambiguity, genome base composition, codon usage and codon reassignment.
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Affiliation(s)
- Manuel A S Santos
- Centre for Cell Biology, Department of Biology, University of Aveiro, 3810-193 Aveiro, Portugal.
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33
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Takai K, Yokoyama S. Roles of 5-substituents of tRNA wobble uridines in the recognition of purine-ending codons. Nucleic Acids Res 2003; 31:6383-91. [PMID: 14602896 PMCID: PMC275538 DOI: 10.1093/nar/gkg839] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2003] [Revised: 09/10/2003] [Accepted: 09/20/2003] [Indexed: 11/14/2022] Open
Abstract
Many tRNA molecules that recognize the purine-ending codons but not the pyrimidine-ending codons have a modified uridine at the wobble position, in which a methylene carbon is attached directly to position 5 of the uracil ring. Although several models have been proposed concerning the mechanism by which the 5-substituents regulate codon-reading properties of the tRNAs, none could explain recent results of the experiments utilizing well-characterized modification-deficient strains of Escherichia coli. Here, we first summarize previous studies on the codon-reading properties of tRNA molecules with a U derivative at the wobble position. Then, we propose a hypothetical mechanism of the reading of the G-ending codons by such tRNA molecules that could explain the experimental results. The hypothesis supposes unconventional base pairs between a protonated form of the modified uridines and the G at the third position of the codon stabilized by two direct hydrogen bonds between the bases. The hypothesis also addresses differences between the prokaryotic and eukaryotic decoding systems.
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Affiliation(s)
- Kazuyuki Takai
- Cell-Free Science and Technology Research Center, Department of Applied Chemistry, Faculty of Engineering, Ehime University, 3, Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
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34
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tRNA1Ser(G34) with the anticodon GGA can recognize not only UCC and UCU codons but also UCA and UCG codons. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1626:75-82. [PMID: 12697332 DOI: 10.1016/s0167-4781(03)00045-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The tRNA1Ser (anticodon VGA, V=uridin-5-oxyacetic acid) is essential for translation of the UCA codon in Escherichia coli. Here, we studied the translational abilities of serine tRNA derivatives, which have different bases from wild type at the first positions of their anticodons, using synthetic mRNAs containing the UCN (N=A, G, C, or U) codon. The tRNA1Ser(G34) having the anticodon GGA was able to read not only UCC and UCU codons but also UCA and UCG codons. This means that the formation of G-A or G-G pair allowed at the wobble position and these base pairs are noncanonical. The translational efficiency of the tRNA1Ser(G34) for UCA or UCG codon depends on the 2'-O-methylation of the C32 (Cm). The 2'-O-methylation of C32 may give rise to the space necessary for G-A or G-G base pair formation between the first position of anticodon and the third position of codon.
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35
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Cabello-Villegas J, Winkler ME, Nikonowicz EP. Solution conformations of unmodified and A(37)N(6)-dimethylallyl modified anticodon stem-loops of Escherichia coli tRNA(Phe). J Mol Biol 2002; 319:1015-34. [PMID: 12079344 DOI: 10.1016/s0022-2836(02)00382-0] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The modification of RNA nucleotide bases, a fundamental process in all cells, alters the chemical and physical properties of RNA molecules and broadly impacts the physiological properties of cells. tRNA molecules are by far the most diverse-modified RNA species within cells, containing as a group >80% of the known 96 chemically unique nucleic acid modifications. The greatest varieties of modifications are located on residue 37 and play a role in ensuring fidelity and efficiency of protein synthesis. The enzyme dimethylallyl (Delta(2)-isopentenyl) diphosphate:tRNA transferase catalyzes the addition of a dimethylallyl group to the exocyclic amine nitrogen (N6) of A(37) in several tRNA species. Using a 17 residue oligoribonucleotide corresponding to the anticodon arm of Escherichia coli tRNA(Phe), we have investigated the structural and dynamic changes introduced by the dimethylallyl group. The unmodified RNA molecule adopts stem-loop conformation composed of seven base-pairs and a compact three nucleotide loop. This conformation is distinctly different from the U-turn motif that characterizes the anticodon arm in the X-ray crystal structure of the fully modified yeast tRNA(Phe). The adoption of the tri-nucleotide loop by the purine-rich unmodified tRNA(Phe) anticodon arm suggests that other anticodon sequences, especially those containing pyrimidine bases, also may favor a tri-loop conformation. Introduction of the dimethylallyl modification increases the mobility of nucleotides of the loop region but does not dramatically alter the RNA conformation. The dimethylallyl modification may enhance ribosome binding through multiple mechanisms including destabilization of the closed anticodon loop and stabilization of the codon-anticodon helix.
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MESH Headings
- Alkyl and Aryl Transferases/metabolism
- Anticodon/chemistry
- Anticodon/genetics
- Anticodon/metabolism
- Base Sequence
- Escherichia coli/genetics
- Hydrogen Bonding
- Magnesium/pharmacology
- Magnetic Resonance Spectroscopy
- Models, Molecular
- Nuclear Magnetic Resonance, Biomolecular
- Nucleic Acid Conformation/drug effects
- Nucleic Acid Denaturation
- Protein Biosynthesis
- RNA, Bacterial/chemistry
- RNA, Bacterial/genetics
- RNA, Bacterial/metabolism
- RNA, Transfer, Phe/chemistry
- RNA, Transfer, Phe/genetics
- RNA, Transfer, Phe/metabolism
- Solutions
- Thermodynamics
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36
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Chen P, Qian Q, Zhang S, Isaksson LA, Björk GR. A cytosolic tRNA with an unmodified adenosine in the wobble position reads a codon ending with the non-complementary nucleoside cytidine. J Mol Biol 2002; 317:481-92. [PMID: 11955004 DOI: 10.1006/jmbi.2002.5435] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Out of more than 500 sequenced cytosolic tRNAs, there is only one with an unmodified adenosine in the wobble position (position 34). The reason for this rare occurrence of A34 is that it is mostly deaminated to inosine-34 (I34). I34 is a common constituent in the wobble position of tRNAs and has a decoding capacity different from that of A34. We have isolated a mutant (proL207) of Salmonella typhimurium, in which the wobble nucleoside G34 has been replaced by an unmodified A in tRNA(Pro)(GGG), which is the only tRNA that normally reads the CCC codon. Thus, this mutant apparently has no tRNA that is considered cognate for the codon CCC. Despite this, the mutant grows normally. As expected, Pro-tRNA selection at the CCC codon in the A-site in a mutant deleted for the proL gene, which encodes the tRNA(Pro)(GGG), was severely reduced. However, in comparison this rate of selection was only slightly reduced in the proL207 mutant with its A34 containing tRNA(Pro)(AGG) suggesting that this tRNA reads CCC. Moreover, measurements of the interference by a tRNA residing in the P-site on the apparent termination efficiency at the A-site indicated that indeed the A34 containing tRNA reads the CCC codon. We conclude that A34 in a cytosolic tRNA is not detrimental to the cell and that the mutant tRNA(Pro)(AGG) is able to read the CCC codon like its wild-type counterpart tRNA(Pro)(GGG). We suggest that the decoding of the CCC codon by a 5'-AGG-3' anticodon occurs by a wobble base-pair between a protonated A34 and a C in the mRNA.
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Affiliation(s)
- Peng Chen
- Department of Molecular Biology, Umeå University, Umeå, 901 87, Sweden
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37
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Kim HS, Kim IY, Söll D, Lee SY. Transfer RNA identity change in anticodon variants of E. coli tRNA(Phe) in vivo. Mol Cells 2000; 10:76-82. [PMID: 10774751 DOI: 10.1007/s10059-000-0076-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
The anticodon sequence is a major recognition element for most aminoacyl-tRNA synthetases. We investigated the in vivo effects of changing the anticodon on the aminoacylation specificity in the example of E. coli tRNA(Phe). Constructing different anticodon mutants of E. coli tRNA(Phe) by site-directed mutagenesis, we isolated 22 anticodon mutant tRNA(Phe); the anticodons corresponded to 16 amino acids and an opal stop codon. To examine whether the mutant tRNAs had changed their amino acid acceptor specificity in vivo, we tested the viability of E. coli strains containing these tRNA(Phe) genes in a medium which permitted tRNA induction. Fourteen mutant tRNA genes did not affect host viability. However, eight mutant tRNA genes were toxic to the host and prevented growth, presumably because the anticodon mutants led to translational errors. Many mutant tRNAs which did not affect host viability were not aminoacylated in vivo. Three mutant tRNAs containing anticodon sequences corresponding to lysine (UUU), methionine (CAU) and threonine (UGU) were charged with the amino acid corresponding to their anticodon, but not with phenylalanine. These three tRNAs and tRNA(Phe) are located in the same cluster in a sequence similarity dendrogram of total E. coli tRNAs. The results support the idea that such tRNAs arising from in vivo evolution are derived by anticodon change from the same ancestor tRNA.
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Affiliation(s)
- H S Kim
- Graduate School of Biotechnology, Korea University, Seoul
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38
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Abstract
Comparative path lengths in amino acid biosynthesis and other molecular indicators of the timing of codon assignment were examined to reconstruct the main stages of code evolution. The codon tree obtained was rooted in the 4 N-fixing amino acids (Asp, Glu, Asn, Gln) and 16 triplets of the NAN set. This small, locally phased (commaless) code evidently arose from ambiguous translation on a poly(A) collector strand, in a surface reaction network. Copolymerisation of these amino acids yields polyanionic peptide chains, which could anchor uncharged amide residues to a positively charged mineral surface. From RNA virus structure and replication in vitro, the first genes seemed to be RNA segments spliced into tRNA. Expansion of the code reduced the risk of mutation to an unreadable codon. This step was conditional on initiation at the 5'-codon of a translated sequence. Incorporation of increasingly hydrophobic amino acids accompanied expansion. As codons of the NUN set were assigned most slowly, they received the most nonpolar amino acids. The origin of ferredoxin and Gln synthetase was traced to mid-expansion phase. Surface metabolism ceased by the end of code expansion, as cells bounded by a proteo-phospholipid membrane, with a protoATPase, had emerged. Incorporation of positively charged and aromatic amino acids followed. They entered the post-expansion code by codon capture. Synthesis of efficient enzymes with acid-base catalysis was then possible. Both types of aminoacyl-tRNA synthetases were attributed to this stage. tRNA sequence diversity and error rates in RNA replication indicate the code evolved within 20 million yr in the preIsuan era. These findings on the genetic code provide empirical evidence, from a contemporaneous source, that a surface reaction network, centred on C-fixing autocatalytic cycles, rapidly led to cellular life on Earth.
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Affiliation(s)
- B K Davis
- Research Foundation of Southern California Inc., La Jolla 92037, USA
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39
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Auffinger P, Westhof E. Singly and bifurcated hydrogen-bonded base-pairs in tRNA anticodon hairpins and ribozymes. J Mol Biol 1999; 292:467-83. [PMID: 10497015 DOI: 10.1006/jmbi.1999.3080] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The tRNA anticodon loops always comprise seven nucleotides and is involved in many recognition processes with proteins and RNA fragments. We have investigated the nature and the possible interactions between the first (32) and last (38) residues of the loop on the basis of the available sequences and crystal structures. The data demonstrate the conservation of a bifurcated hydrogen bond interaction between residues 32 and 38, located at the stem/loop junction. This interaction leads to the formation of a non-canonical base-pair which is preserved in the known crystal structures of tRNA/synthetase complexes. Among the tRNA and tDNA sequences, 93 % of the 32.38 oppositions can be assigned to two families of isosteric base-pairs, one with a large (86 %) and the other with a much smaller (7 %) population. The remainder (7 %) of the oppositions have been assigned to a third family due to the lack of evidence for assigning them into the first two sets. In all families, the Y32.R38 base-pairs are not isosteric upon reversal (like the sheared G.A or wobble G.U pairs), explaining the strong conservation of a pyrimidine at position 32. Thus, the 32.38 interaction extends the sequence signature of the anticodon loop beyond the conserved U-turn at position 33 and the usually modified purine at position 37. A comparison with other loops containing both a singly hydrogen-bonded base-pair and a U-turn suggests that the 32.38 pair could be involved in the formation of a base triple with a residue in a ribosomal RNA component. It is also observed that two crystal structures of ribozymes (hammerhead and leadzyme) present similar base-pairs at the cleavage site.
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Affiliation(s)
- P Auffinger
- Modélisations et Simulations des Acides Nucléiques, UPR 9002, Institut de Biologie Moléculaire et Cellulaire du CNRS, 15 rue René Descartes, Strasbourg Cedex, 67084, France
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40
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Burger G, Saint-Louis D, Gray MW, Lang BF. Complete sequence of the mitochondrial DNA of the red alga Porphyra purpurea. Cyanobacterial introns and shared ancestry of red and green algae. THE PLANT CELL 1999; 11:1675-94. [PMID: 10488235 PMCID: PMC144311 DOI: 10.1105/tpc.11.9.1675] [Citation(s) in RCA: 111] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The mitochondrial DNA (mtDNA) of Porphyra purpurea, a circular-mapping genome of 36,753 bp, has been completely sequenced. A total of 57 densely packed genes has been identified, including the basic set typically found in animals and fungi, as well as seven genes characteristic of protist and plant mtDNAs and specifying ribosomal proteins and subunits of succinate:ubiquinone oxidoreductase. The mitochondrial large subunit rRNA gene contains two group II introns that are extraordinarily similar to those found in the cyanobacterium Calothrix sp, suggesting a recent lateral intron transfer between a bacterial and a mitochondrial genome. Notable features of P. purpurea mtDNA include the presence of two 291-bp inverted repeats that likely mediate homologous recombination, resulting in genome rearrangement, and of numerous sequence polymorphisms in the coding and intergenic regions. Comparative analysis of red algal mitochondrial genomes from five different, evolutionarily distant orders reveals that rhodophyte mtDNAs are unusually uniform in size and gene order. Finally, phylogenetic analyses provide strong evidence that red algae share a common ancestry with green algae and plants.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Chlorophyta/genetics
- Chromosome Mapping
- Codon/genetics
- Cyanobacteria/genetics
- DNA, Bacterial/genetics
- DNA, Mitochondrial/genetics
- DNA-Directed DNA Polymerase/genetics
- Introns
- Molecular Sequence Data
- Nucleic Acid Conformation
- Phylogeny
- Plants/genetics
- Polymorphism, Genetic
- Pseudogenes
- RNA, Ribosomal, 5S/chemistry
- RNA, Ribosomal, 5S/genetics
- RNA, Transfer/genetics
- Reading Frames
- Recombination, Genetic
- Repetitive Sequences, Nucleic Acid
- Rhodophyta/genetics
- Sequence Homology, Amino Acid
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Affiliation(s)
- G Burger
- Program in Evolutionary Biology, Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, Ontario M5G 1Z8, Canada.
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41
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Mejlhede N, Atkins JF, Neuhard J. Ribosomal -1 frameshifting during decoding of Bacillus subtilis cdd occurs at the sequence CGA AAG. J Bacteriol 1999; 181:2930-7. [PMID: 10217788 PMCID: PMC93739 DOI: 10.1128/jb.181.9.2930-2937.1999] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During translation of the Bacillus subtilis cdd gene, encoding cytidine deaminase (CDA), a ribosomal -1 frameshift occurs near the stop codon, resulting in a CDA subunit extended by 13 amino acids. The frequency of the frameshift is approximately 16%, and it occurs both when the cdd gene is expressed from a multicopy plasmid in Escherichia coli and when it is expressed from the chromosomal copy in B. subtilis. As a result, heterotetrameric forms of the enzyme are formed in vivo along with the dominant homotetrameric species. The different forms have approximately the same specific activity. The cdd gene was cloned in pUC19 such that the lacZ' gene of the vector followed the cdd gene in the -1 reading frame immediately after the cdd stop codon. By using site-directed mutagenesis of the cdd-lacZ' fusion, it was shown that frameshifting occurred at the sequence CGA AAG, 9 bp upstream of the in-frame cdd stop codon, and that it was stimulated by a Shine-Dalgarno-like sequence located 14 bp upstream of the shift site. The possible function of this frameshift in gene expression is discussed.
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Affiliation(s)
- N Mejlhede
- Center for Enzyme Research, Institute of Molecular Biology, University of Copenhagen, DK-1307 Copenhagen K, Denmark
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42
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Takai K, Takaku H, Yokoyama S. In vitro codon-reading specificities of unmodified tRNA molecules with different anticodons on the sequence background of Escherichia coli tRNASer. Biochem Biophys Res Commun 1999; 257:662-7. [PMID: 10208840 DOI: 10.1006/bbrc.1999.0538] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The codon-reading properties of wobble-position variants of the unmodified form of Escherichia coli tRNASer1 (the UGA anticodon) were measured in a cell-free translation system. Two variants, with the AGA and CGA anticodons, each exclusively read a single codon, UCU and UCG, respectively. The only case of efficient wobbling occurred with the variant with the GGA anticodon, which reads the UCU codon in addition to the UCC codon. Surprisingly, this wobble reading is more efficient than the Watson-Crick reading by the variant with the AGA anticodon. Furthermore, we prepared tRNA variants with AA, UC, and CU, instead of GA, in the second and third positions and measured their relative efficiencies in the reading of codons starting with UU, GA, and AG, respectively. The specificity concerning the wobble position is essentially the same as that in the case of the codons starting with UC.
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Affiliation(s)
- K Takai
- Department of Industrial Chemistry, Chiba Institute of Technology, 2-17-1, Tsudanuma, Narashino, Chiba, 275-0016, Japan
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43
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Krüger MK, Pedersen S, Hagervall TG, Sørensen MA. The modification of the wobble base of tRNAGlu modulates the translation rate of glutamic acid codons in vivo. J Mol Biol 1998; 284:621-31. [PMID: 9826503 DOI: 10.1006/jmbi.1998.2196] [Citation(s) in RCA: 96] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In Escherichia coli, uridine in the wobble position of tRNAGlu and tRNALys is modified to mnm5s2U34. This modification is believed to restrict the base-pairing capability, i.e. to prevent misreading of near-cognate codons and reduce the efficiency of cognate codon reading, especially of codons ending in G. We have determined the influence of the 5-methylaminomethyl and the 2-thio modifications of mnm5s2U34 in tRNAGlu on the translation rate of the glutamate codons GAA and GAG in vivo. In wild-type cells, GAG is translated slower (7. 7 codons/second) and GAA faster (18 codons/second) than the average codon (13 codons/second). Surprisingly, tRNAGlu lacking the 5-methylaminomethyl group, thus containing s2U34, translated GAA twofold faster (47 codons/second) and GAG fourfold slower (1.9 codons/second) than fully modified tRNAGlu. In contrast, tRNAGlu that contains mnm5U34 instead of mnm5s2U34 translated GAA fourfold slower (4.5 codons/second) and GAG only 20% slower (6.2 codons/second). Clearly, the 5-methylaminomethyl group of mnm5s2U34 facilitates base-pairing with G while decreasing base-pairing with A, resulting in rates of translation of GAG and GAA that approach that of the average codon. The 2-thio group increases the recognition of GAA and has only a minor effect on the decoding of GAG. Furthermore, the 2-thio group is important for aminoacylation (see the accompanying paper). These data imply that the function of mnm5s2U34 may be different from what has been suggested previously.
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Affiliation(s)
- M K Krüger
- Department of Molecular Cell Biology, University of Copenhagen, Denmark
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44
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Tsai F, Curran JF. tRNA(2Gln) mutants that translate the CGA arginine codon as glutamine in Escherichia coli. RNA (NEW YORK, N.Y.) 1998; 4:1514-1522. [PMID: 9848650 PMCID: PMC1369722 DOI: 10.1017/s1355838298981274] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
We present a novel missense suppression system for the selection of tRNA(2GIn) mutants that can efficiently translate the CGA (arginine) codon as glutamine. tRNA(2Gln) mutants were cloned from a partially randomized synthetic gene pool using a plasmid vector that simultaneously expresses the tRNA gene and, to ensure efficient aminoacylation, the glutamine aminoacyl-tRNA synthetase gene (glnS). tRNA mutants that insert glutamine at CGA were selected as missense suppressors of a lacZ mutant (lacZ625(CGA)) that contains CGA substituted for an essential glutamine codon. Preliminary characterizations of four suppressors is presented. All of them contain two anticodon mutations: C-->U at position 34 and U-->C at position 35, which allow for cognate translation of CGA. U35 was previously shown to be an important determinant for glutaminylation of tRNA(2Gln) in vitro; suppression in vivo requires overexpression of the glutaminyl-tRNA synthetase gene (glnS). One tRNA variant contains no further mutations and has the highest missense suppression activity (8%). Three other isolates each contain an additional point mutation that alters suppression efficiency. This system will be useful for further studies of tRNA structure and function. In addition, because relatively efficient translation of the rare CGA codon as glutamine is not toxic for Escherichia coli, it may be possible to translate this sense codon with other alternate meanings, a property which could greatly facilitate protein engineering.
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Affiliation(s)
- F Tsai
- Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA
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Hagervall TG, Pomerantz SC, McCloskey JA. Reduced misreading of asparagine codons by Escherichia coli tRNALys with hypomodified derivatives of 5-methylaminomethyl-2-thiouridine in the wobble position. J Mol Biol 1998; 284:33-42. [PMID: 9811540 DOI: 10.1006/jmbi.1998.2162] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It has been suggested that modified nucleosides of the xm5(s2)U(m)34-type restrict the wobble capacity of the base, and that their function is to prevent misreading in the third position of the codon in mixed codon family boxes that encode two different amino acids. In this study in Escherichia coli, the misreading in vivo of asparagine codons in bacteriophage MS2 mRNA by different hypomodified derivatives of tRNALys, normally containing 5-methylaminomethyl-2-thiouridine (mnm5s2U34) in the wobble position, has been analysed. Contrary to what would be predicted from the general hypothesis for the function of mnm5s2U, it was found that the misreading of asparagine codons by tRNALys was greatly reduced in the mnmA (formerly asuE or trmU) and mnmE (formerly trmE) mutants which contain the hypomodified mnm5U34 and s2U34, respectively, instead of the fully modified mnm5s2U34. In addition, it was found that these hypomodified tRNAs were efficiently charged with lysine in vivo, under the growth conditions employed. The latter result is at variance with results obtained in vitro. The results are discussed in relation to the postulated function for modified nucleosides of the xm5s2U type.
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Affiliation(s)
- T G Hagervall
- Department of Microbiology, Umeå University, Umeå, S-901 87, Sweden.
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Abstract
tRNAGly1 is the Escherichia coli glycine tRNA specific for GGG codons. A genetic selection for multicopy suppressors of a frameshift mutation has shown that increased levels of wild-type tRNAGly1 causes -1 frameshifting. Analysis of the suppression spectrum of this multicopy suppressor and peptide sequencing of the suppressed protein product showed that it promoted GG doublet decoding at the near-cognate GGA codons. It is proposed that increasing the concentration of the GGG-specific tRNAGly1 relative to the cognate GGA-decoding tRNAGly2 allows the near-cognate tRNA to read GGA codons. Near-cognate decoding of GGA codons by tRNAGly1 can occur by a two-out-of-three reading mechanism, in which only the first two bases of the GGA codon are paired with the anticodon, thus permitting doublet translocations. In mycoplasmas, a single tRNA typically decodes all four triplets of a codon family and introduction of a feature of the Mypoplasma mycoides tRNAGly responsible for non-discriminate decoding, a C at position 32, into the anticodon E. coli tRNAGly1, enhanced the efficiency of doublet decoding.
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Affiliation(s)
- M O'Connor
- J.W. Wilson Laboratory, Department of Molecular and Cellular Biology and Biochemistry, Brown University, Providence, RI 02912, USA
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Takai K, Takaku H, Yokoyama S. Codon-reading specificity of an unmodified form of Escherichia coli tRNA1Ser in cell-free protein synthesis. Nucleic Acids Res 1996; 24:2894-9. [PMID: 8760870 PMCID: PMC146040 DOI: 10.1093/nar/24.15.2894] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Unmodified tRNA molecules are useful for many purposes in cell-free protein biosynthesis, but there is little information about how the lack of tRNA post-transcriptional modifications affects the coding specificity for synonymous codons. In the present study, we prepared an unmodified form of Escherichia coli tRNA1Ser, which originally has the cmo5UGA anticodon (cmo5U = uridine 5-oxyacetic acid) and recognizes the UCU, UCA and UCG codons. The codon specificity of the unmodified tRNA was tested in a cell-free protein synthesis directed by designed mRNAs under competition conditions with the parent tRNA1Ser. It was found that the unmodified tRNA with the UGA anti-codon recognizes the UCA codon nearly as efficiently as the modified tRNA. The unmodified tRNA recognized the UCU codon with low, but detectable efficiency, whereas no recognition of the UCC and UCG codons was detected. Therefore, the absence of modifications makes this tRNA more specific to the UCA codon by remarkably reducing the efficiencies of wobble reading of other synonymous codons, without a significant decrease in the UCA reading efficiency.
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Affiliation(s)
- K Takai
- Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Japan
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Curran JF, Poole ES, Tate WP, Gross BL. Selection of aminoacyl-tRNAs at sense codons: the size of the tRNA variable loop determines whether the immediate 3' nucleotide to the codon has a context effect. Nucleic Acids Res 1995; 23:4104-8. [PMID: 7479072 PMCID: PMC307350 DOI: 10.1093/nar/23.20.4104] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Codon context can affect translational efficiency by several molecular mechanisms. The base stacking interactions between a codon-anticodon complex and the neighboring nucleotide immediately 3' can facilitate translation by amber suppressors and the tRNA structure is also known to modulate the sensitivity to context. In this study the relative rates of aminoacyl-tRNA selection were measured at four sense codons (UGG, CUC, UUC and UCA), in all four 3' nucleotide contexts, through direct competition with a programmed frameshift at a site derived from the release factor 2 gene. Two codons (UGG and UUC) are read by tRNAs with small variable regions and their rates of aminoacyl-tRNA selection correlated with the potential base stacking strength of the 3' neighboring nucleotide. The other two codons (CUC and UCA) are read by tRNAs with large variable regions and the rate of selection of the aminoacyl-tRNAs in these cases varied little among the four contexts. Re-examination of published data on amber suppression also revealed an inverse correlation between context sensitivity and the size of the variable region. Collectively the data suggest that a large variable loop in a tRNA decreases the influence of the 3' context on tRNA selection, probably by strengthening tRNA-ribosomal interactions.
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Affiliation(s)
- J F Curran
- Department of Biology, Wake Forest University, Winston-Salem, NC 27109, USA
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Schneider A, McNally KP, Agabian N. Nuclear-encoded mitochondrial tRNAs of Trypanosoma brucei have a modified cytidine in the anticodon loop. Nucleic Acids Res 1994; 22:3699-705. [PMID: 7524027 PMCID: PMC308349 DOI: 10.1093/nar/22.18.3699] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The mitochondrial genome of Trypanosoma brucei does not appear to encode any tRNA genes. Isolated organellar tRNAs hybridize to nuclear DNA, suggesting that they are synthesized in the nucleus and subsequently imported into the mitochondrion. Most imported tRNAs have cytosolic counterparts, showing identical mobility on two-dimensional polyacrylamide gels. We have compared three nuclear-encoded mitochondrial tRNAs (tRNA(Lys), tRNA(Leu), tRNA(Tyr)) with their cytosolic isoforms by direct enzymatic sequence analysis. Our findings indicate that the primary sequences of the mitochondrial and the corresponding cytosolic tRNAs are identical. However, we have identified a mitochondrion-specific nucleotide modification of each tRNA which is localized to a conserved cytidine residue at the penultimate position 5' of the anticodon. The modification present in mature mitochondrial tRNA(Tyr) was not found in a mutant tRNA(Tyr) defective in splicing in either cytosolic or mitochondrial fractions. The mutant tRNA(Tyr) has been expressed in transformed cells and its import into mitochondria has been demonstrated, suggesting that the modified cytidine residue is not required for import and therefore may be involved in adapting imported tRNAs to specific requirements of the mitochondrial translation machinery.
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Affiliation(s)
- A Schneider
- Intercampus Program in Molecular Parasitology, University of California, San Francisco 94143-1204
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